Herpes simplex virus 1 and 2 (HSV-1 and HSV-2) are two species of the herpesvirus family, herpesviridae, which cause infections in humans. Human herpesvirus infections cause a variety of illnesses including cold sores, chickenpox or varicella, shingles or herpes zoster (VZV), cytomegalovirus (CMV), mononucleosis (EBV) and various cancers, and can cause brain inflammation (encephalitis). All viruses in the herpes family produce life-long infections. HSV-1 and HSV-2 are also called Human Herpesvirus 1 and 2 (HHV-1 and HHV-2) and belong to the sub-family of neurotropic herpesviruses, which are conventionally referred to as the alpha-herpesviruses. Like all alpha-herpesviruses, HSV-1 and HSV-2 present two stages of infection: active infection and latent infection. In the active infection stage, the infected individual is symptomatic for HSV infection. In the latent infection stage, the virus becomes dormant in the nervous system of their host, which accounts for the ability of the virus to persist. An infected individual can experience multiple cycles of active and latent infection.
HSV-1 is commonly associated with recurrent herpes outbreaks of the face known as cold sores or fever blisters, whereas HSV-2 is more often associated with recurrent genital herpes.
An infection by a herpes simplex virus (HSV) is marked by watery blisters in the skin or mucous membranes of the mouth, lips, genitals or anus and buttocks. Lesions heal with a scab characteristic of herpetic disease. However, the infection is persistent and symptoms may recur periodically as outbreaks of sores near the site of original infection. After the initial, or primary, infection, HSV becomes latent in the cell bodies of nerves in the area. Some infected people experience sporadic episodes of viral reactivation, followed by transportation of the virus via the nerve's axon to the skin or mucosa, where virus replication and shedding occurs. Herpes is contagious if the carrier is producing and shedding the virus. This is especially likely during a symptomatic outbreak, but possible at other times. There is no cure yet, but there are treatments which reduce the likelihood of viral shedding.
HSV-1 is a common and significant human pathogen which causes a variety of diseases, ranging from cold sores to potentially blinding ocular infections and life-threatening encephalitis. HSV-1 establishes lifelong latent infections in neuronal cells, which reactivate periodically. Latent infection is defined as a lack of production of infectious virus at the site. Productive infection can be characterized by the expression of nearly all (about 100) viral genes in epithelial cells and fibroblasts at the periphery and the sensory neurons that innervate the site of infection.